The number of babies who survive after being born extremely early is rising, as are those very premature infants who make it to three years of age without a major disability, two studies show.

Overall survival among babies born between 22 and 25 weeks rose significantly from 40% in 1995 to 53% in 2006, according to one of the research papers published by the British Medical Journal. The number of such newborns admitted to neonatal intensive care over the same period also rose from 666 in 1995 to 1,115 in 2006, reflecting advances in neonatal medicine.

And by the end of the same period, 11% more babies were making it to three years old without any of the disabilities often associated with very premature birth, such as cerebral palsy or learning disabilities, according to the other study, both of which were funded by the Medical Research Council.

Most babies who are born that early in pregnancy die and many of those who survive have often profound lifelong disability and require intensive care and support.

Almost one in 12 (7.8%) babies in the UK – about 60,000 – are born before 37 weeks' gestation. Rates of prematurity are rising by about 1.5% a year. Experts do not know why but pregnant women who smoke or are overweight or eat an unhealthy diet while carrying their child are at higher risk of delivering early.

However, although an extremely premature baby's chances of survival have risen, the same research also found the proportion of such infants who experience severe disability as a result has not changed. That stood at 18% in 1995 and was 19% in 2006, according to the research.

"Our findings show that more babies now survive being born too soon than ever before, which is testament to the highly-skilled and dedicated staff in our neonatal services", said Professor Neil Marlow, an MRC-funded academic at University College London's Institute for Women's Health and a co-author of both papers. "But as the number of children that survive pre-term birth continues to rise, so will the number who experience disability throughout their lives. This is likely to have an impact on the demand for health, education and social care services."

The increased chance of survival is due to obstetricians giving steroids to more mothers-to-be who are thought likely to imminently give birth to an extremely premature baby, in order to boost the child's lungs before birth, and neonatologists' improved ability to help very premature newborns to breathe, said Jane Brewin, chief executive of the baby charity Tommy's. The studies reached their findings after comparing the medical history and outcomes of babies born between 22 and 26 weeks' gestation in 2006 in England with a group born between 22 and 25 weeks in 1995.

A Department of Health spokeswoman said: "Whilst it is good news that more children are surviving premature birth, we need to make sure that sick and premature babies get consistently high quality neonatal care and support for any disabilities. The government has taken action to reduce premature births, but it's also important that women have personalised care throughout their pregnancy."

"Midwives provide vital personalised, one to one care and there are now almost over 900 more midwives working in the NHS than there were in 2010."